This patent application is a continuation-in part patent application of U.S. patent application Ser. No. 09/020 898 filed on Feb. 9, 1998 and claiming priority of German patent application No. 197 06 867.7 filed on Feb. 21, 1997. These two patent applications are declared an integral part of the present patent application.
This invention relates to a method for the generation of a single- or multi-start grinding worm for grinding tooth profiles in accordance with the principle of continuous diagonal generation grinding, and an apparatus for implementing this method, by which across a portion of the worm width the flanks of the worm thread are given modifications, and the ratio between the modified and the non-modified grinding worm zone yields an optimum with respect to a favorable exploitation of the overall worm width.
The majority of cylindrical gears used in gear drive technology today have involute tooth profiles. However, for load reasons, the meshing of two involute gears often fails to produce an optimal operating behavior, so the tooth flanks are provided with modifications deviating from the involute, in both the profile and longitudinal directions by means of design calculations. As the magnitude of such modifications for the most part falls within the micrometric range, grinding processes play an essential role in the manufacture of modified tooth flanks.
The more straightforward modifications of tooth flanks consist primarily of profile or longitudinal crowning, tip or root relief in relation to profile and end relief in relation to face width If we view these modifications in terms of their variation in the two tooth flank directions (tooth depth and face width), we can see that they are tooth flank modifications that always change in the one tooth flank direction only, while remaining constant in the second tooth flank direction. In continuous generating grinding, these modifications can be achieved either by means of profiling of the grinding tool with special profiling tools (generally profile modifications) or by means of appropriate movement of the machine axes (generally longitudinal modifications). In the latter case, these additional axial movements during continuous generating grinding often result in unwanted distortion of the tooth flank profile.
In contrast, the application of more complicated tooth flank modifications requires varying specifications in a number of transverse sections and on a number of cylinders. In extreme cases, each point on the flank of the tooth can be allotted its own modification magnitude (deviation of the profile from the involute). The manufacture of such gearing by means of continuous generation grinding requires special technological procedures.
The state of the art for the profiling of grinding worms remains an important factor in arriving at a solution. In the known processes in this respect (FIG. 1) a disk-shaped profiling tool 1 is often used. This profiling tool is shifted in a translatory linear stroke 3 relative to a rotating grinding worm 2 during which the profiling tool contacts the tip and/or the root of one or both flanks of the grinding worm thread 4. The stroke action 3 of the profiling tool and the rotational movement 5 of the grinding worm 2 are precisely attuned to one another, so that after one revolution of the worm the profiling tool has traveled a path as xcfx80 * module * number of starts. Of the multitude of procedural specifications applied in this regard, two general principles are known.
When profiling with a profile roll (FIG. 1a), the active zone 6 of the disk-shaped profiling tool 1 has a single-tapered or double-tapered profile. During the profiling procedure, this shape leads to line contact between the profiling tool 1 and a normal section of the grinding worm thread 4. The advantage of this contact relationship is that the entire depth of the grinding worm thread (h), including the root and tip zones, can be. profiled with a single translatory stroke 3 of the profiling tool or of the grinding worm 2 across the width of the grinding worm (b5). The result is short profiling times. As with this method a large portion of the flank depth of a worm thread axial section is always engaged (generally the entire profile), it will be referred to hereinafter as profile dressing.
Profiling with a universal roll (FIG. 1b) uses a disk-shaped profiling tool having, for example, a radius profile in the active zone 6. With this tool, the contact between the profiling tool 1 and the grinding worm thread is almost punctiform. Thus, only a very limited portion of the grinding worm thread depth (h) is profiled during each stroke 3 across the width of the grinding worm (b5). A multitude of profiling strokes is needed to profile the entire grinding worm thread, the profiling tool being infed by a defined amount (xcex94U) into the grinding worm thread depth after each stroke. This profiling method leads to long profiling times, particularly in the case of grinding worms with large modules. However, it is also known that, because of the point contact in the zone of contact, this method is very advantageous for the generation of virtually any desired modifications down the profile grinding worm thread profile. In the following text, this method will be referred to as line-by-line profiling.
In a known process for producing complicated tooth flank modifications in generation grinding, the grinding tool is tangentially displaced in relation to the gear during the working stroke (shifting or diagonal generative grinding) (DE 3704607). A special feature of this generation grinding process is that, because of the tangential shift during the cutting stroke, a new line of action between the gear and the grinding worm can be allocated to every gear normal section. By the use of a grinding worm that has a worm thread of continually changing pressure angle across its entire active width, the aforementioned process compensates for process-related distortion of the tooth flank. This distortion occurs during the continuous generation grinding of helical gears if the center distance between the workpiece and the tool changes during the working stroke (e.g., when producing longitudinal crowning). A disadvantage of this procedure is that the grinding worm receives altered pressure angles (modifications) across its entire active width, and hence, when grinding worms are used with conventional abrasives, there is increased wear in those worm zones where grinding proceeds at higher metal removal rates. On the other hand, if non-profilable grinding worms with super-hard abrasives are used, the flexible profiling of the grinding worm thread with new pressure angle changes (modifications) is not possible.
In regard to line-by-line profiling, a process is known (Wo 95/24989) in which, according to the tooth flank modifications to be generated, a grinding worm is provided with different modifications in various width zones. Applying line-by-line profiling of the grinding worm, these individual width zones are given modifications down the profile of the thread which differ from zone to zone but remain constant within a given zone. Between the individual width zones of the grinding worm, there are transitional zones in which a transition occurs between the thread profile modification of one width zone and the thread profile modification of the following width zone. The generation of continuous flank modifications in the direction of worm width and, consequently, in the gear tooth longitudinal direction, is not possible with this process.
Beginning with the known state of the art (as described above), the task presented is to provide a grinding worm with a geometry and flank topology which, on the one hand, permit high metal removal rates and on the other hand, permit the generation of tooth flank modifications on the micrometric level. This task, in turn, entails a need to develop methods or a combination of these methods which allow for flexible profiling of grinding worms with modified thread flanks. In doing so, we must also decide which modifications of the grinding worm thread flanks can be generated with which profiling method or with which combination of profiling methods, with due consideration for the quality demands on the gearing to be ground, and for the goal of minimizing profiling time. Finally, an apparatus must be developed which can be used to execute the profiling process or combination of profiling processes.
The solution to this task is based on the two known fundamental methods for profiling grinding worms, viz.: profile dressing and line-by-line dressing, as well as on the diagonal generation grinding of gears.